1. Field of the Invention
The present invention generally relates to an image forming device. More specifically, the present invention relates to an image forming device having a thermal head.
2. Background Information
A conventional sublimation type image forming device includes a thermal head having a printing head. With the conventional image forming device, an ink ribbon is superposed with recording paper composed of printer paper. The ink ribbon is coated with a sublimation dye. Electrical energy corresponding to image information is applied to the thermal head. The thermal energy generated by the thermal head causes the sublimation dye to sublimate and be transferred to the recording paper, such as special printer paper, thereby performing specific printing, such as color printing. With the conventional image forming device, rendering of an image with gradation is accomplished by controlling amounts of current sent to the thermal head, that is, amounts of heat generated by the printing head.
Another conventional image forming device includes a frame, a bushing, a platen roller and a thermal head (see Japanese Laid-Open Utility Model Application No. 2001-8, for example). The thermal head has a heat sink (heat radiating plate). The bushing is fitted to a protrusion provided to the heat sink. The bushing is latched to a latching portion of the frame. The thermal head contacts or separates from the platen roller.
Another conventional image forming device includes a frame, a thermal head substrate and a heat radiating plate. The heat radiating plate is joined to the thermal head substrate. A bearing provided to the heat radiating plate is engaged with a support shaft provided to the frame (see Japanese Laid-Open Patent Application No. H11-321013, for example).
With the conventional image forming devices, however, in printing, the printing head of the thermal head has to be positioned in a specific location with respect to the platen roller. Accordingly, the conventional image forming devices include a hinge portion, such as a latching portion or an engagement portion, for supporting the thermal head. The hinge portion is provided along a printing direction of the printing head so as to prevent position changes of the printing head due to frictional force during printing. Therefore, restrictions on the layout of parts, such as not being able to insert an ink ribbon cartridge from a side face of the frame, are imposed. These restrictions cause less latitude in design.
On the other hand, another conventional image forming device includes a side plate, a thermal head, a heat radiating plate, a curved head movement member and a platen roller (see Japanese Laid-Open Patent Application No. H11-254715, for example). The heat radiating plate is attached to the side plate via the curved head movement member so that an ink ribbon cartridge is inserted through a hole formed on the side plate. With the conventional image forming device, a hinge portion of the thermal head is provided along a printing direction of a printing head of the thermal head.
However, the conventional image forming device requires the curved head movement members and a fixing member, such as a screw, to attach the heat radiating plate to the curved head movement member. Also, since the thermal head is supported by combining the head movement member and the heat radiating plate, it is difficult to position the printing head of the thermal head with respect to the platen roller, which makes it difficult to render high-quality images. To solve the problem, the conventional image forming device further includes a reference positioning mechanism. The reference positioning mechanism has a reference positioning groove and an eccentric member for positional adjustment. The reference positioning groove is provided to the heat radiating plate and a thermal head attachment base of the thermal head. As a result, the conventional image forming device increases the number of parts required. Furthermore, the conventional image forming device also increases the number of assembly steps. Therefore, the cost of the conventional image forming device increases.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved image forming device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.